Recombinant tissue-type plasminogen activator is superior to streptokinase for local intra-arterial thrombolysis

Potential Benefits from Heating the High-Dose rtPA Boluses Used in Catheter-Directed Thrombolysis for Acute/Subacute Lower Limb Ischemia

Purpose:

To explore the potential benefits from heating recombinant tissue plasminogen activator (rtPA) before catheter-directed thrombolysis in patients with lower-limb ischemia of <30 days' duration.

Methods:

Over a 2-year period, 34 patients (26 men; mean age 63.5 years, range 39–80) with 10 iliac and 24 infrainguinal arterial occlusions (5 embolic and 29 thrombotic) were treated with two 5-mg boluses of rtPA injected into the proximal clot, followed by 2 additional 5-mg boluses of rtPA. In the first 18 patients (group A), room temperature rtPA was administered, whereas in the last 16 patients (group B), the rtPA boluses were heated to 38°C for 30 minutes before injection. Residual thrombus was treated with a continuous infusion of 2.5 mg/h of rtPA for 4 hours then at a reduced dose (1 mg/h).

Results:

Successful thrombolysis was achieved in 28 (82%) arteries. Unmasked lesions were treated with balloon angioplasty/stenting in 17 cases and with surgery in 4. One fatal retroperitoneal hematoma occurred in group A. Heating the rtPA did not significantly alter the outcome of thrombolysis. However, a statistically significant reduction in the total rtPA dose was observed in group B (24.28 mg versus 27.9 mg in group A, p = 0.05), as well as quicker lysis (2 hours, 42 minutes versus 6 hours, 12 minutes in group A, p = 0.001). There was no statistical difference in the amputation-free survival at 30 days between the groups.

Conclusions:

In patients with acute or subacute lower limb ischemia treated with catheter-directed thrombolysis, heating the rtPA results in faster lysis with a considerable reduction in the total dose of the lytic agent.

Review of pharmacology and physiology in thrombolysis interventions

Reperfusion therapy using thrombolytic agents has been shown to be a safe and effective treatment strategy for arterial ischemia, venous thrombosis, massive pulmonary embolism, and acute stroke. Thrombolytic agents have evolved over the course of a few decades, from nonfibrin selective to fibrin-selective agents. The development and modification of these agents have resulted in improved understanding of their pharmacologic attributes, and their effects on the complex molecular events that occur during thrombolysis goal-directed therapies. The current review focuses on the physiology and pharmacology of the thrombolytic agents that have been or are currently in use for interventional thrombolysis interventions. Attention is also given to the particular role that thrombolytic agents play in the current management of peripheral vascular disease and acute stroke.

Catheter-directed thrombolysis for acute limb ischemia

Acute limb ischemia is a potentially life-threatening clinical event. Thrombosis in situ, bypass graft thrombosis, and embolic occlusion are the three major precipitating events leading to acute limb ischemia. Management of acute ischemia depends on the clinical status of the affected limb and patient comorbidities. Catheter-directed thrombolysis (CDT) is the treatment of choice for patients with relatively mild acute limb ischemia (Rutherford categories I and IIa) with no contraindications to thrombolytic therapy. Patients with severe acute limb ischemia (Rutherford category IIb) need emergent revascularization. CDT should be considered, nonetheless, if the relative risks compared with primary operation are favorable. CDT is a life- and limb-saving treatment for many patients despite limitations of efficacy and associated complications. This article is a review of the etiology of acute arterial occlusion; clinical triage of patients presenting with acute limb ischemia; catheter guide wire techniques, pharmacological agents, and devices in current use for CDT; as well as the outcomes of CDT.

Usefulness of catheter-directed thrombolysis using alteplase in peripheral vascular occlusion

This study evaluated the safety and efficacy of alteplase in catheter-directed treatment for peripheral arterial and venous thrombosis and considered the optimal dosing regimen. Forty-four patients (49 encounters) underwent transcatheter therapy using alteplase between January and November 1999. The most common indications for thrombolysis were peripheral arterial occlusion (PAO) and venous thrombosis (38 patients, 43 encounters). Each encounter was reviewed for indication, dosage of alteplase, duration of infusion, concomitant use of anticoagulation, degree of lysis, and complications. Patients were divided into low-dose (0.5 to 1.0 mg/hr), mid-dose (1.0 to 1.5 mg/hr), and high-dose (>1.5 mg/hr) groups. For PAO, there was no significant difference in the success rate between the 3 dose groups. A lower complication rate was achieved in the low-dose group. For venous thrombosis, there was no difference in the overall success or complication rates for each of the 3 groups. Partial lysis was achieved more readily in the mid and high-dose groups, but the risk of serious complications was greater. Overall, the complete thrombolysis rate was 71% for PAO and 55% for venous thrombosis. Major and minor complication rates were 7% and 19%, respectively. An equivalent success rate with a lower complication rate can be achieved using a low-dose constant catheter-directed infusion of alteplase for cases of PAO. Cases of venous thrombosis had a lower overall success rate compared with PAO. A mid-dose infusion of alteplase can achieve greater complete and partial thrombolysis rates without increasing the complication rate. Major and minor complication rates were similar to the rates given in the published literature.

Safety of Thrombolytic Therapy with Urokinase or Recombinant Tissue Plasminogen Activator for Peripheral Arterial Occlusion:A Comprehensive Compilation of Published Work

PURPOSE

To report a comprehensive literature review focused on comparing the risk of complications with urokinase versus recombinant tissue plasminogen activator (rtPA) for thrombolytic treatment of peripheral arterial occlusions.

METHODS

The English-language literature between 1985 and 2002 was searched for studies that used tissue-derived urokinase or rtPA in the treatment of peripheral arterial occlusions. Forty-eight studies (22 urokinase, 22 rtPA, and 4 that included both treatments) were identified, encompassing 2226 urokinase-treated patients and 1927 rtPA-treated patients. The safety of each thrombolytic agent was assessed based on the incidence of major hemorrhage, intracerebral hemorrhage, major limb amputation, transfusions, and mortality.

RESULTS

The review revealed a wide range of study protocols, patient conditions, ages of occlusions, dosages/delivery methods of lytic agents, and criteria for reporting complications. The incidence of major hemorrhage varied widely, but the overall rate was lower among urokinase-treated patients (6.2%) than for patients treated with rtPA (8.4%, p=0.007). The overall incidence of intracerebral hemorrhage was also significantly lower for urokinase (0.4% versus 1.1% for rtPA, p=0.020). The major amputation rate was similar for both treatments (urokinase 7.9%, rtPA 7.2%), but the mortality rate was significantly lower for urokinase (3.0% versus 5.6% for rtPA, p<0.001). The need for transfusions was less frequent with urokinase (11.1% versus 16.1%, p=0.002).

CONCLUSIONS

These results from a large body of published literature suggest that urokinase may be associated with a lower incidence of complications than rtPA in the treatment of peripheral arterial occlusions.

Thrombolysis in the Management of Lower Limb Peripheral Arterial Occlusion—A Consensus Document

The aim of this paper is to develop an intercontinental consensus on the use of thrombolytic therapy in occlusive peripheral arterial disease affecting lower limbs. A working party of self-designated angiologists, hematologists, interventional radiologists, and vascular surgeons of Europe and North America convened at 4 closed meetings. All published data known to any of the participants was entered into discussion. The working party discussed the topics outlined in this paper and a first draft was prepared in segments by members of the working party, discussed, and further revised into an interim report. It was then circulated to a number of Societies for their input. A final meeting of the Working Party together with delegates of the Societies collaborated on the definitive version of the text. The Party appreciates that in many areas the scientific evidence is not yet available. Nevertheless, it was felt that enough practical and scientific data were available to establish recommendations for clinical practice as well as for reporting results of thrombolytic therapy, which could be updated as later evidence became available. The guidelines apply only to drugs currently available for clinical use. The data are also considered to be sufficiently cogent that regulatory agencies should move to approve thrombolytic agents for intra-arterial therapy of acute lower extremity ischemia.

The management of acute limb ischemia: techniques for dealing with thrombus

Acute limb ischemia (ALI) has long been a major clinical problem, producing significant risks for limb loss and death. It is most commonly caused by arterial thrombosis in the setting of underlying atherosclerotic peripheral vascular disease or by arterial embolism, usually of cardiac origin. Over the past several decades, preferred treatment options for ALI have alternated between medical and surgical approaches. More recently, direct intra-arterial thrombolysis became the standard of care after several randomized trials demonstrated the benefit of this approach as compared with acute surgical intervention. Despite all of the experience with direct intra-arterial thrombolysis for the treatment of ALI, the optimal thrombolytic approach not been clearly established. Current investigation is directed at identifying the ideal thrombolytic agent for this purpose and the appropriate dosing regimen. In addition, there is interest in the newer mechanical thrombectomy devices and the use of platelet glycoprotein IIb/IIIa inhibitors to speed the time to reperfusion of the acutely ischemic limb.

Transcatheter intraarterial infusion of rt-PA for acute lower limb ischemia: results and complications

PURPOSE

To determine the success and complication rates of intraarterial recombinant tissue-type plasminogen activator (rt-PA) infusion for the treatment of acute lower extremity artery and bypass graft occlusions.

MATERIALS AND METHODS

The results of 74 limbs in 70 patients (mean age, 66 y) treated with catheter-directed rt-PA infusion for the treatment of acute lower extremity ischemia were retrospectively evaluated. The group included 42 bypass grafts and 32 native arteries. All limbs were viable at presentation. The mean duration of symptoms was 11.9 days. rt-PA was infused for a mean of 27.9 hours for a mean total dose of 38.7 mg. Initial infusion rates of 3-6 mg/h were lowered to a preferred rate of 1.5 mg/h. Thrombolytic success was defined as 95% thrombolysis of an occluded segment with return of antegrade flow. Major bleeding complications were defined as any hemorrhagic event leading to surgery, extended or unexpected hospitalization, transfusion, death, intracranial hemorrhage, or a decrease in hemoglobin of 5 g/dL or in hematocrit of 15%. Thirty-day mortality and amputation rates were calculated. Patient characteristics and infusion parameters were evaluated as to whether they contributed to thrombolytic success or major bleeding events.

RESULTS

Thrombolytic success was achieved in 64 limbs (86%). Major bleeding complications occurred in 33 (47%) patients. In 22 of these patients, bleeding occurred at a vascular puncture site, whereas remote bleeding occurred in seven patients. Remote bleeding complications included two retroperitoneal hematomas, two rectus sheath hematomas, one lower gastrointestinal hemorrhage, one episode of hemoptysis, and one dehiscence of a femoral-popliteal bypass graft revision. No parameters were found to be predictive of thrombolytic success, whereas a negative history of smoking, increasing duration of infusion, and a low preprocedural ankle-brachial index (ABI) were found to be associated with major hemorrhagic events. Four patients (6%) underwent amputation and one patient (1%) died, resulting in a 30-day amputation-free survival rate of 93%.

CONCLUSION

Catheter-directed rt-PA infusion is effective in achieving thrombolysis. Despite a significant number of bleeding complications, 30-day mortality and amputation rates were favorable. Nonetheless, complication rates related to bleeding were not trivial and further evaluation with use of variable dosing regimens is indicated.

Thrombolytic therapy with use of alteplase (rt-PA) in peripheral arterial occlusive disease: review of the clinical literature. The Advisory Panel

PURPOSE

The clinical literature describing the use of alteplase in the treatment of peripheral arterial occlusive (PAO) disease is reviewed.

MATERIALS AND METHODS

The literature database was acquired by a MEDLINE search using the Boolean keyword string: tissue plasminogen activator and/or rt-PA and peripheral not animal. A review was performed to identify the dose range of alteplase, technique of infusion, use of anticoagulation, clinical success rates, and risk of complications.

RESULTS

Forty-six clinical studies were identified. There are few prospective, randomized clinical trials and a lack of standardized protocols and endpoints. Use of catheter-directed infusions of recombinant tissue plasminogen activator (rt-PA) may be beneficial versus surgery in the initial management of acute limb ischemia (< 14 days) and in reducing the magnitude of subsequent surgical or percutaneous revascularization. For patients with chronic limb ischemia (> 14 days), irreversible acute limb ischemia, or advanced diabetic arteriopathy, catheter-directed infusion of rt-PA or other plasminogen activators may be unsuitable. The risk of adverse bleeding appears related to the overall dose and duration of infusion. These risks appear similar to those of urokinase. The role of heparin in increasing adverse bleeding during rt-PA therapy is unclear.

CONCLUSIONS

There is no generally accepted dose or technique for administering catheter-directed thrombolysis using alteplase; however, several studies have demonstrated its clinical safety and efficacy. Formal studies will be required to determine the optimal dose, technique of infusion, the role of anticoagulation, and complication rates when alteplase is used for PAO disease.

Local recombinant tissue plasminogen activator (rt-PA) thrombolytic therapy in microvascular surgery

Vascular thrombosis remains a dreaded complication of any microvascular procedure, be it composite tissue transfer or replantation of amputated limbs or parts. Despite the tremendous advances in microvascular-related technologies and the accumulated surgical skills, failures caused by occlusion of anastomosed vessels remain a continuous source of frustration to all microsurgeons alike. Several anticoagulation and antiplatelet protocols have been proposed to be used in conjunction with microvascular surgery. More recently, thrombolytic drugs such as urokinase, streptokinase, and thrombolysin have been introduced, yet their systemic effect on hemostasis remains an undesirable side effect. We present our experience with local intra-arterial, intravenous, and soft-tissue injection of recombinant tissue plasminogen activator rt-PA in replantation surgery in three consecutive patients. Arterial thrombi are managed by intra-arterial rt-PA infusion with the catheter placed proximal to the arterial anastomosis. Venous thrombi are best lysed by infusing rt-PA in an engorged vein of the replanted limb. In replanted digits, direct intravenous infusion is not possible. In such situations, injection of rt-PA in the pulp soft tissues may result in successful salvage. We believe this agent also has a role in microvascular composite tissue transfer in preventing free flap failures as well as in salvaging failing flaps.

Age-related outcome for peripheral thrombolysis

OBJECTIVES

To investigate the age-related outcome of peripheral thrombolysis and determine for which patient group this treatment is worthwhile.

DESIGN AND METHODS

A combined retrospective and prospective analysis of consecutive patients undergoing thrombolysis for acute lower-limb ischaemia was made with respect to age-related outcome and other risk factors.

RESULTS

One hundred and two patients underwent thrombolysis for acute limb ischaemia. In the under 60 age group there was a 40% amputation rate. Seventy-three per cent of this group smoked. In the over 80 age group, the amputation rate was 15% and only 8% were smokers.

CONCLUSION

Advancing age is not an adverse risk factor for thrombolysis which appears to be safe and effective in this patient group. There is a high incidence of smoking in the younger age group (< 60 years), in whom failed thrombolysis frequently leads to amputation.

Assessing clot lysis strategies using a simplified mathematical model

This paper attempts to describe lysis of a clot by infusion of lytic agent using a simple geometrical approach, in which the rate of clot lysis is assumed proportional to the exposed surface of the clot and the concentration of lytic agent. Six simple realizations (a)-(f) of this basic model are developed which account for the dependence of clot lysis time on five different clot geometries. In all six cases the clot is initially described as a uniform cylinder which totally occludes a vessel. In model (a) lysis proceeds as an advancing front at the proximal face of the clot. In model (b) lysis proceeds radially outwards from the central axis of the vessel while in model (c) lysis occurs radially inwards from the surface adjacent the wall, of the cylinder. In models (d) and (e) it is assumed that the clot breaks into a uniform spherical and cylindrical fragments, respectively, while model (f) uses the spherical fragment model combined with a lytic agent concentration which decreases with time. The validity of the models was assessed using previously published data from 76 patients in whom lysis time and clot size were recorded. Least squares linear regression analysis based on the six model equations yielded highly significant correlation coefficients r2 of 0.457, 0.412, 0.412, 0.495, 0.469, 0.663 for models (a)-(f), respectively. The results suggest that when a constant lytic agent concentration is assumed, no single geometry accounts for significantly more variation than any other, but that a combination of varying lytic agent concentration and clot geometry significantly influences clot lysis time and accounts for much of the observed variation.

Intra-arterial thrombolysis for the acutely ischaemic leg: experience in a district general hospital

Intra-arterial thrombolytic therapy (IATT) is a recognized treatment for acute on chronic lower limb ischaemia due to thrombosis when duration of therapy will not compromise limb viability. In this prospective study at a district general hospital, 36 consecutive patients (mean age 73.6 +/- 1.7 years) with acute lower limb ischaemia, presenting as severe and worsening claudication or rest pain, underwent urgent IATT using streptokinase (n = 35) or tPA (n = 1). Thrombolysis was monitored by daily angiography. IATT was performed alone in 26 patients and in conjunction with angioplasty in a further 10 patients. Mean treatment duration was 2.27 + 0.25 days. The 30 day mortality was 11.1% Complications abbreviated IATT in 8.3%. The 30 day primary limb salvage rate for IATT +/- angioplasty was 44.4% (16/36). The mean ABPI pre IATT +/- angioplasty was 0.19 +/- 0.04(n = 35) compared with 0.52 +/- 0.08 after IATT +/- angioplasty (n = 31) (P < 0.011). Eight patients without clinical benefit underwent salvage surgery with a secondary limb salvage rate of 61%. ABPI post-salvage surgery was similarly increased to 0.54 +/- 0.17. Intra-arterial thrombolytic therapy for the acutely ischaemic leg in a district general hospital, may contribute to limb salvage.

Factors predicting the outcome of intraarterial thrombolysis in peripheral arterial and graft occlusions

PURPOSE

To determine the association between successful intraarterial thrombolysis and the following factors: sex, age, symptoms, duration of symptoms, length of occlusion, conduit type, runoff, and catheter localization.

MATERIAL AND METHODS

Forty-six patients with acute or subacute occlusions of peripheral native arteries and grafts were treated with continuous intraarterial infusion of streptokinase or urokinase. A univariate chi-square test and logistic regression analysis were used.

RESULTS

Successful lysis was achieved in 27 of 46 patients (59%). The logistic regression analysis revealed a significant association between successful thrombolysis and good runoff (p < 0.01). A catheter position above the occlusion resulted in lysis in only one of 11 patients. The variables rest pain and claudication were slightly significant (p = 0.07). None of the other variables were significant, but a trend toward a separate effect of duration of occlusion was found.

CONCLUSION

Good runoff and intrathrombotic infusion are virtual necessities in obtaining a positive immediate outcome in peripheral arterial and graft occlusions. In our study, other factors were less important.

Thrombolysis with prourokinase versus urokinase: an in vitro comparison

PURPOSE

Despite advantages demonstrated in vitro, no single thrombolytic agent has been clearly shown to be superior to another in the clinical setting. Prourokinase has recently received attention as a new thrombolytic agent with higher fibrin specificity. The thrombolytic activity of prourokinase, however, remains ill defined. The purpose of this study was to evaluate thrombolysis with prourokinase in comparison to urokinase in vitro.

METHODS

We used an in vitro parallel channel perfusion model that simulates catheter-directed thrombolysis in the peripheral arterial system. Radiolabeled thrombi were subjected to 90 minutes of endhole catheter-directed infusion with either prourokinase 5000 IU/ml, urokinase 5000 IU/ml; or 5% dextrose in water at 4 ml/hr.

RESULTS

Prourokinase and urokinase were found to be equivalent with respect to thrombolytic effect. Percent lysis was maximal at 90 minutes in both the urokinase and prourokinase groups. Prourokinase and urokinase were found to be equally effective in restoring flow through thrombosed graft segments.

CONCLUSION

Prourokinase appears to offer little benefit over urokinase with respect to thrombolytic activity in an in vitro model that closely resembles the clinical setting. If prourokinase is to be accepted as an alternative to urokinase, advantages must relate to differences in fibrin specificity.

Accelerated thrombolysis with high dose bolus t-PA extends the role of peripheral thrombolysis but may increase the risks

Low dose intra-arterial thrombolysis is too slow for many patients with severe acute limb ischaemia. Accelerated thrombolysis with high dose bolus t-PA was used in a consecutive series of 43 patients. Complete or clinically useful lysis was achieved in 39 patients, with a median duration of 7 h. Lysis occurred in 46% in under 4 h. Fifty-six per cent of patients required further procedures after lysis. Eleven per cent suffered a major bleed. The limb salvage rate at 30 days was 56%. Amputation was required in 22% and 22% died. Most deaths were due to associated thrombotic conditions: myocardial infarction (5), pulmonary embolism (1) and malignant thrombosis (1). One patient died from pneumonia two weeks after lysis and two died from renal failure within a week of thrombolysis. The high mortality rate was not associated with bleeding but may reflect the high risks involved in treating this group of patients. High dose bolus t-PA infusion appears to predict immediate outcome of thrombolysis as well as reducing infusion times. It may expand the indications for the non-surgical treatment of acute limb ischaemia to include most patients with the condition. Careful case selection is still necessary for optimal results.

Prospective randomised comparative study of pulse spray and conventional local thrombolysis

OBJECTIVES

To compare the time required to achieve lysis with the pulse spray technique and the conventional slow continuous infusion technique.

DESIGN

Prospective randomised open Study.

METHODS

Eighteen patients suitable for intra-arterial thrombolytic therapy with conventional and pulse spray technique were randomised 1:1 to receive either pulse spray thrombolysis with 0.33 mg/ml rt-PA injected as a bolus of 0.2 ml or conventional thrombolysis with 0.05 mg/ml rt-PA infused at a rate of 10 ml/h.

RESULTS

The age, duration of symptoms, length of occlusion and prethrombolysis ankle brachial pressure index were comparable in the two groups. The median duration of thrombolytic therapy in the pulse spray group was 195 min (range 90-1260) compared to 1390 min (range 300-2400) in the Conventional group. The difference between the two groups was significant, p < 0.002 (Mann-Whitney test).

CONCLUSIONS

Significantly shorter time is required to achieve local thrombolysis with pulse spray compared to the conventional infusion method.

Lower limb intra-arterial thrombolysis

In the UK, approximately 5000 patients present annually with acute lower limb ischaemia. The aetiology is usually thromboembolic disease, other causes include aortic dissection and arterial trauma. Over the past two decades thrombosis has replaced embolism as the principal cause of acute ischaemia, and now accounts for approximately 59% of cases. As a consequence, intra-arterial thrombolysis is being increasingly used as first-line treatment for this condition.

Immediate and early follow-up results of purse spray thrombolysis in patients with peripheral ischaemia

Pulse spray thrombolysis is a technique of accelerated peripheral thrombolysis which has been evaluated in 38 patients, 29 with threatened limb viability and nine with a viable but critically ischaemic limb. The median length of occlusion was 26.5 (range 3-65) cm. The lytic agent used was recombinant tissue plasminogen activator (rtPA), injected manually via a pulse spray catheter at a concentration of 0.33 mg/ml and a bolus size of 0.2 ml. The median total dose of rtPA was 18 (range 5-35)mg. Patency and flow were completely restored in 34 of 38 patients and clinical success at 30 days was maintained in 27 of 38. The median lysis time was 120 (range 35-1125) min, compared with a median duration of 1545 (range 42-5760) min in 120 consecutive patients previously treated with conventional low-dose infusion thrombolysis using rtPA. This represents a 12-fold reduction in lysis time (P < 0.001). The overall estimated cumulative limb salvage rate for the 38 patients who entered the study was 84 per cent and the cumulative patency rate for the 34 patients in whom patency was restored was 74 per cent at 18 months follow-up. Pulse spray thrombolysis rapidly restores patency with good limb salvage at 30 days; the benefit is sustained even in patients with limbs at immediate risk of irreversible ischaemic injury who are not considered suitable for conventional thrombolysis.

Thrombolysis with tissue-plasminogen activator: results with a high-dose transthrombus technique

PURPOSE

Low-dose intraarterial tissue plasminogen activator (t-PA) is effective in peripheral thrombolysis but treatment time is prolonged. The aim of this study was to determine whether a transthrombus bolus of t-PA before low-dose infusion shortens lysis time.

METHODS

Twenty-three patients with peripheral arterial or bypass graft occlusion were treated with an initial bolus of 20 mg t-PA followed by a continuous infusion of 1 mg/hr.

RESULTS

Angiographic lysis was achieved in 16 patients (70%) with a mean time to complete lysis of 14.4 +/- 7.9 hours. Two patients had reocclusion on days 1 and 3, respectively. There were three deaths within the first week of treatment, one from cerebral hemorrhage and two from myocardial infarction. A clinically successful outcome was achieved in 11 patients (48%). Those patients with patency at 1 week maintained this response at a mean follow-up of 11.7 +/- 9.1 months. Thrombolysis was unsuccessful in seven instances. In three of these cases the infusion had to be discontinued prematurely because of serious hemorrhage. Of the seven unsuccessful cases, three patients subsequently underwent a femorodistal bypass, two were left with tolerable ischemic symptoms, and two required a major amputation. There were eight major bleeding complications (35%), four at or adjacent to the catheter entry site and four at a distance, including two cases of cerebral hemorrhage, one of which was fatal.

CONCLUSIONS

Transthrombus bolus delivery of tissue plasminogen activator followed by a low-dose infusion shortens lysis time, but this technique appears to be associated with an increased risk of serious hemorrhage.

Long-term results of a single protocol for thrombolysis in acute lower-limb ischaemia

In a prospective study, 78 of 157 patients with acute lower-limb ischaemia were considered suitable for thrombolysis. The immediate and 4-year results of 52 patients managed by a single protocol are reported. Of 34 patients alive at 4 years, 23 had limb salvage. Initial treatment produced effective lysis in 38 patients (73 per cent) with significant benefit in 35 (67 per cent); that benefit was sustained for a minimum of 4 years in 30 patients (58 per cent). Seven of the 18 deaths by 4 years occurred within 30 days. Amputation was carried out in six patients within 30 days and in five during the next 4 years. Delayed amputation followed persistent distal occlusion or progression of distal disease. No death or amputation was caused by complication of treatment. In selected patients the risks of thrombolysis can be reduced to an acceptable level by personal supervision and a strict protocol. In survivors, limb salvage is generally sustained for at least 4 years.

Acute limb deterioration during intra-arterial thrombolysis

Approximately 12 per cent of limbs undergoing intra-arterial thrombolysis (IAT) develop distal embolism or extension of thrombus during the procedure. These are usually of little clinical consequence and can be treated by increasing the rate of administration of the lytic agent. However, in some patients the clinical condition of the limb deteriorates rapidly. In an attempt to define the incidence of acute limb deterioration during IAT, information was collected from five centres in the UK with experience of the technique. A total of 866 treatments were recorded, with 20 limbs (2.3 per cent) undergoing acute deterioration. This complication was more common during the treatment of thrombosed popliteal aneurysm than during that of emboli or thrombosed atheromatous arteries or grafts (P < 0.001). The amputation rate associated with the complication was high, and operative intervention provided better results than continuation of lysis.

Early results and 1-year follow-up after intra-arterial thrombolysis

Intra-arterial thrombolysis (IAT) was used as first-line treatment for 100 occlusions causing acute, subacute or chronic ischaemia. Streptokinase was used in 90 cases and tissue plasminogen activator in the remaining ten. Complete lysis, as determined radiologically, was achieved in 55 per cent of cases and partial lysis in 20 per cent. Lysis was more effective the earlier it was used. Major complications occurred in seven cases: five patients suffered major haemorrhage, two of whom died, and two had haemorrhagic cerebrovascular accidents. Of the patients with complete or partial clearance of thrombosis, 19 had no underlying apparent cause, 23 underwent angioplasty and 15 had an operation. The 1-year patency rate following complete lysis was 58 per cent. The 1-year patency rate after successful treatment commencing within 1 week of symptoms starting was 71 per cent, compared with 36 per cent for later treatment. Aortofemoral bifurcation grafts were cleared in three of five cases and all remain patent. Eight popliteal aneurysms were demonstrated by IAT and were ligated and bypassed; all these grafts remained patent at follow-up. IAT is less effective in chronic than acute occlusion. It should be reserved for patients in whom the occlusion is of short duration or for those with a thrombosed aortofemoral bifurcation graft or popliteal aneurysm.

Platelet Imaging in Man using Antiplatelet Monoclonal Antibodies

Radiolabeled platelets have been used in experimental imaging studies using the gamma camera to localize and quantify platelet accumulation. Conventional radiolabelling methods have been laborious, requiring specialized expertise and facilities. Recent advances in biotechnology have provided a number of murine monoclonal antibodies for the selective radiolabelling of circulating cells, cellular components and proteins. Most of these antibodies have been used for the in vitro study of platelet membrane structures. Relatively few antibodies have been administered to humans for in vivo imaging. Nevertheless, the use of monoclonal antibodies as a means of in vivo radiolabelling of platelets following a single intravenous injection represents a significant advance over the established techniques. Clinical studies currently underway have demonstrated that antibodies specific for platelets have the potential for replacing the conventional methods of radiolabelling and can result in images of outstanding quality. This paper reviews the current experimental and clinical studies using antibodies specific for platelets. In the main, these antibodies bind to the platelet membrane glycoprotein complexes IIb/IIIa or Ia/IIa. Recently, however, an antibody binding to P-selectin, and therefore specific to activated platelets, has been introduced and represents an interesting new development. The future application of this technology based on either humanized or synthetic molecules recognizing platelet antigens is likely to become routinely accepted for the study of platelet deposition in experimental settings and for thrombus imaging in clinical practice.

Choice of agent for peripheral thrombolysis

Evidence has been accumulating that tissue plasminogen activator (tPA) is a more rapid and effective agent than streptokinase for peripheral thrombolysis. Twenty-three patients with acute limb-threatening ischaemia treated with tPA (0.5 mg h-1) over 15 months were compared with 20 consecutive patients previously receiving streptokinase (5000-10,000 units h-1). There were no major differences between the rates of complete and partial lysis (61 per cent for tPA versus 65 per cent for streptokinase) or limb salvage (65 versus 55 per cent respectively). Complication rates were also similar. It was not possible to show that tPA, an agent ten times more expensive than streptokinase, was superior for peripheral thrombolysis.